Method for producing oxide catalyst and method for producing unsaturated nitrile

ABSTRACT

The present invention relates to a method for producing an oxide catalyst containing Mo, V, Sb, and Nb, the method including a raw material preparation step of obtaining an aqueous mixed liquid containing Mo, V, Sb, and Nb, an aging step of subjecting the aqueous mixed liquid to aging at more than 30° C., a drying step of drying the aqueous mixed liquid, thereby obtaining a dried powder, and a calcination step of calcining the dried powder, thereby obtaining the oxide catalyst, and a method for producing an unsaturated nitrile or an unsaturated acid by using the catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of co-pending applicationSer. No. 16/332,732, filed on Mar. 12, 2019, which is the National Phaseunder 35 U.S.C. § 371 of International Application No.PCT/JP2017/032564, filed on Sep. 8, 2017, which claims the benefit under35 U.S.C. § 119(a) to Patent Application No. 2016-178885, filed in Japanon Sep. 13, 2016, all of which are hereby expressly incorporated byreference into the present application.

TECHNICAL FIELD

The present invention relates to a method for producing an oxidecatalyst and a method for producing an unsaturated nitrile.

BACKGROUND ART

Currently, unsaturated nitriles generally sold on the market are for themost part industrially produced through a catalytic ammoxidationreaction of an olefin, ammonia, and oxygen. On the other hand, in recentyears, a method for producing an unsaturated nitrile corresponding to araw material, the method using as the raw material an alkane such aspropane or isobutane in place of the olefin and using a gas-phasecatalytic ammoxidation reaction, has been drawing attention, and a largenumber of catalysts for use on that occasion have also been proposed.

For example, Patent Literature 1 describes a method for producing, as acatalyst for a gas-phase catalytic oxidation or gas-phase catalyticammoxidation of propane or isobutane, a catalyst containing: at leastone clement selected from tellurium and antimony; molybdenum; vanadium;and niobium, in which a niobium raw material liquid containing niobiumand a carboxylic acid is used.

In addition, as a catalyst for gas-phase catalytic oxidation orgas-phase catalytic ammoxidation of propane or isobutane, PatentLiterature 2 describes a method for producing a catalyst containing: atleast one element selected from tellurium and antimony; molybdenum;vanadium; and niobium, wherein precipitation of a niobium compound isprevented in a catalyst-producing step by adding a complex-forming agentsuch as hydrogen peroxide to a niobium raw material liquid.

In addition, Patent Literature 3 describes a method for producing acatalyst containing molybdenum, vanadium, and niobium, in which anaqueous mixed liquid containing the above-described elements issubjected to aging for 90 minutes or more and 50 hours or less under anatmosphere having an oxygen concentration of 1 to 25 vol %.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No. 3938225-   Patent Literature 2: Japanese Patent No. 4666334-   Patent Literature 3: Japanese Patent Laid-Open No. 2009-183897

SUMMARY OF INVENTION Technical Problem

However, according to the methods for producing a catalyst described inPatent Literatures 1 to 3, an ammoxidation reaction catalyst capable ofenduring the use under particular conditions is obtained, but it cannotbe deemed that the yield of an unsaturated nitrile, in a case where theresultant catalyst is used, is industrially sufficient. Further, thereis a need for keeping a state in which all the components are uniformlydispersed in a solution containing a catalyst raw material whilesuppressing precipitation of Nb, which is a component that is hardlysoluble, at the time of producing a catalyst, and therefore there is thefollowing problem: it takes a long time to produce a catalyst.

The present invention has been made in consideration of the problems ofthe above-described conventional techniques, and an object of thepresent invention is to provide a method by which an oxide catalystgiving a high unsaturated nitrile yield can be obtained, and further,the oxide catalyst can be produced in a relatively short time withoutthe need for introducing a complicated step and changing facilities.

Solution to Problem

The present inventors have conducted diligent studies to solve theproblems of the conventional techniques to find that by following amethod for producing an oxide catalyst, which is used for gas-phasecontact oxidation or gas-phase contact ammoxidation of propane orisobutane and comprises particular components, comprises: a raw materialpreparation step; an aging step; a drying step; and a calcination step,wherein precipitation of niobium is facilitated in the preparation stepand/or the aging step, an oxide catalyst exhibiting high performance canbe produced in a relatively short time, thereby completing the presentinvention.

That is, the present invention is as follows.

1. A method for producing an oxide catalyst comprising Mo, V, Sb, andNb, the method comprising:

a raw material preparation step of obtaining an aqueous mixed liquidcomprising Mo, V, Sb, and Nb;

an aging step of subjecting the aqueous mixed liquid to aging at morethan 30° C.;

a drying step of drying the aqueous mixed liquid, thereby obtaining adried powder; and

a calcination step of calcining the dried powder, thereby obtaining theoxide catalyst,

wherein, in the raw material preparation step and/or the aging step,precipitation of Nb is facilitated by performing at least one operationselected from the group consisting of the following (I) to (III):

-   -   (I) in the raw material preparation step, the aqueous mixed        liquid is prepared by mixing a Nb raw material liquid comprising        Nb with a MoVSb raw material liquid comprising Mo, V, and Sb,        wherein ammonia is added to at least one of the MoVSb raw        material liquid, the Nb raw material liquid, and the aqueous        mixed liquid such that a molar ratio in terms of NH₃/Nb in the        aqueous mixed liquid is adjusted to be 0.7 or more, and in the        aging step, a temperature of the aqueous mixed liquid is        adjusted to more than 50° C.;    -   (II) in the aging step, a temperature of the aqueous mixed        liquid is adjusted to more than 65° C.; and    -   (III) in the raw material preparation step, the aqueous mixed        liquid is prepared by mixing a Nb raw material liquid comprising        Nb with a MoVSb raw material liquid comprising Mo, V, and Sb,        wherein a molar ratio in terms of H₂O₂/Nb in the Nb raw material        liquid is adjusted to less than 0.2, and in the aging step, a        temperature of the aqueous mixed liquid is adjusted to more than        50° C.

2. The method for producing the oxide catalyst according to 1, whereinthe oxide catalyst has a composition represented by the followingformula (1):

MoV_(a)Sb_(b)Nb_(c)Z_(d)O_(n)   (1)

wherein Z represents at least one element selected from the groupconsisting of W, La, Ce, Yb, and Y; a, b, c, and d represent values inthe ranges of 0.01≤a≤0.35, 0.01≤b≤0.35, 0.01≤c≤0.20, and 0.00≤d≤0.10,respectively; and n represents a value satisfying a balance of atomicvalences.

3. The method for producing the oxide catalyst according to 1 or 2,wherein the oxide catalyst comprises 30% by mass or more and 70% by massor less of a carrier based on a total amount of the oxide catalyst.

4. A method for producing an unsaturated nitrile, the method comprising:a step of obtaining the oxide catalyst by the method for producing theoxide catalyst according to any of 1 to 3; and a production step ofproducing an unsaturated nitrile through a gas-phase catalyticammoxidation reaction of propane or isobutane in a presence of theproduced oxide catalyst.

5. A method for producing an unsaturated acid, the method comprising: astep of obtaining the oxide catalyst by the method for producing theoxide catalyst according to any of 1 to 3; and a production step ofproducing an unsaturated acid through a gas-phase catalytic oxidationreaction of propane or isobutane in a presence of the produced oxidecatalyst.

Advantageous Effects of Invention

According to the method for producing an oxide catalyst of the presentinvention, an oxide catalyst giving a high unsaturated nitrile yield canbe obtained, and further, the oxide catalyst can be produced in arelatively short time without the need for introducing a complicatedstep and changing facilities.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment for carrying out the present invention(hereinafter, simply referred to as “present embodiment”) will bedescribed in detail. The present embodiment, which will be describedbelow, is an example for describing the present invention and is notintended to limit the present invention to the following contents. Thepresent invention can be carried out by being appropriately modifiedwithin the range of the scope thereof.

[Method for Producing Oxide Catalyst]

A method for producing an oxide catalyst according to the presentembodiment is a method for producing an oxide catalyst comprising Mo, V,Sb, and Nb, and comprises: a raw material preparation step of obtainingan aqueous mixed liquid (hereinafter, also referred to as “aqueous mixedliquid (N)”) comprising Mo, V, Sb, and Nb; an aging step of subjectingthe aqueous mixed liquid to aging at more than 30° C.; a drying step(hereinafter, also referred to as “step (c)”) of drying the aqueousmixed liquid, thereby obtaining a dried powder; and a calcination step(hereinafter, also referred to as “step (d)”) of calcining the driedpowder, thereby obtaining the oxide catalyst, wherein in the rawmaterial preparation step and/or the aging step, precipitation of Nb isfacilitated by performing at least one operation selected from the groupconsisting of the following (I) to (III), namely an operation offacilitating precipitation of Nb is performed on the aqueous mixedliquid (N):

(I) in the raw material preparation step, the aqueous mixed liquid isprepared by mixing a Nb raw material liquid comprising Nb with a MoVSbraw material liquid comprising Mo, V, and Sb, wherein ammonia is addedto at least one of the MoVSb raw material liquid, the Nb raw materialliquid, and the aqueous mixed liquid such that a molar ratio in terms ofNH₃/Nb in the aqueous mixed liquid is adjusted to be 0.7 or more, and inthe aging step, a temperature of the aqueous mixed liquid is adjusted tomore than 50° C.;

(II) in the aging step, a temperature of the aqueous mixed liquid isadjusted to more than 65° C.; and

(III) in the raw material preparation step, the aqueous mixed liquid isprepared by mixing a Nb raw material liquid comprising Nb with a MoVSbraw material liquid comprising Mo, V, and Sb, wherein a molar ratio interms of H₂O₂/Nb in the Nb raw material liquid is adjusted to less than0.2, and in the aging step, a temperature of the aqueous mixed liquid isadjusted to more than 50° C.

According to the method for producing an oxide catalyst of the presentembodiment, which is constituted in this way, an oxide catalyst giving ahigh unsaturated nitrile yield can be obtained, and further, the oxidecatalyst can be produced in a relatively short time without the need forintroducing a complicated step and changing facilities. The oxidecatalyst obtained by the production method according to the presentembodiment can be used suitably for a gas-phase catalytic oxidationreaction or gas-phase catalytic ammoxidation reaction of propane orisobutane.

In the raw material preparation step and/or the aging step in thepresent embodiment, the operation of facilitating precipitation of Nb isperformed on the aqueous mixed liquid (N) as described above.“Precipitation of Nb is facilitated” is not particularly limited as longas Nb in the aqueous mixed liquid is precipitated to accelerateconversion of the aqueous mixed liquid into the form of a slurry, andcan be performed, for example, through aspects of (I) to (III), whichwill be described in detail later. It is to be noted that precipitationof Nb can be checked, for example, by the oxidation-reduction potentialof the aqueous mixed liquid, and it can be deemed that the precipitationis facilitated when a drop in the oxidation-reduction potential becomesfast. More specifically, it can be determined that precipitation of Nbhas been facilitated when the oxidation-reduction potential of a mixedliquid (hereinafter, also referred to as “mixed liquid for measurement”)of an aqueous mixed liquid (A), (A′), or (A″) and an aqueous mixedliquid (N₀) or (N₁), which will be described later, satisfies at leastone of the following a) and b) in a period of continuous 30 minutes fromthe time immediately after mixing until the time immediately beforespray-drying (hereinafter, also referred to as “target period”).

-   a) The potential of the mixed liquid for measurement at the point in    time when the target period starts is lower than the potential of a    standard liquid at the point in time when the target period starts,    and the potential of the mixed liquid for measurement at the point    in time when the target period ends is lower than the potential of    the standard liquid at the point in time when the target period    ends.-   b) The amount of potential dropped, A, calculated as a difference    between the value of the potential of the mixed liquid for    measurement at the point in time when the target period starts and    the potential of the mixed liquid for measurement at the point in    time when the target period ends exceeds 1.2 times the amount of    potential dropped, B, calculated as a difference between the value    of the potential of the standard liquid at the point in time when    the target period starts and the potential of the standard liquid at    the point in time when the target period ends.

The “standard liquid” herein means an aqueous mixed liquid preparedunder the same preparation conditions as in Comparative Example 1, whichwill be described later, namely an aqueous mixed liquid containing Mo,V, Sb, and Nb, the aqueous mixed liquid being obtained by addinghydrogen peroxide water to the Nb raw material liquid in an amount of2.0 in terms of H₂O₂/Nb without adding NH₃ water. In this context, thestandard liquid is prepared in such a way as to obtain an oxide catalysthaving the same composition as the oxide catalyst to be an object ofevaluation with respect to the content of each metal element in thestandard liquid. In addition, the “standard aging temperature” means 55°C. which is the temperature for aging carried out in ComparativeExample 1. It is to be noted that the standard liquid is prepared bymixing the two aqueous mixed liquids at the simultaneous timing ofpreparing the mixed liquid for measurement, and the aging of thestandard liquid is continued under the temperature condition which isthe same as that in Comparative Example 1.

In the present embodiment, the amount of potential dropped, A,preferably exceeds 1.5 times the amount of potential dropped, B, andmore preferably exceeds 2 times in the above-described b) from theviewpoint of moderately facilitating precipitation of Nb.

In the present embodiment, the raw material preparation step can includea preparation step (hereinafter, also referred to as “step (a)”) whichis a sub-step of preparing a MoVSb raw material liquid (hereinafter,also referred to as “aqueous mixed liquid (A)”) comprising Mo, V, andSb. In addition, the raw material preparation step can include a mixingstep (hereinafter, also referred to as “step (b)”) which is a sub-stepof mixing the aqueous mixed liquid (A), the Nb raw material liquidcomprising Nb, and, if necessary, a carrier raw material, therebyobtaining an aqueous mixed liquid (hereinafter, also referred to as“aqueous mixed liquid (N)”; or also referred to as “aqueous mixed liquid(B)” in particular when the aqueous mixed liquid further comprises acarrier raw material) comprising Mo, V, Sb, and Nb. Step (a) and step(b) will be described in detail later.

Further, the method for producing an oxide catalyst according to thepresent embodiment may further comprise a removal step (hereinafter,also referred to as “step (e)”) of removing a protrusion existing at thesurface of a particle of the oxide catalyst. Step (e) will be describedin detail later.

In the present embodiment, “high unsaturated acrylonitrile yield” meansthat in a case where oxide catalysts each at least having the samecomposition as the composition represented by formula (1), which will bedescribed later, are used, the yield of resultant unsaturatedacrylonitrile is high.

[Step (a): Preparation Step]

In step (a) in the present embodiment, the aqueous mixed liquid (A)comprising Mo, V, and Sb is prepared. Examples of the preparation methodinclude, but are not limited to, a method of mixing a Mo-containing rawmaterial (hereinafter, also referred to as “Mo raw material”), aV-containing raw material (hereinafter, also referred to as “V rawmaterial”), and an Sb-containing raw material (hereinafter, alsoreferred to as “Sb raw material”), thereby preparing the aqueous mixedliquid (A). In addition, the method of mixing is not particularlylimited, and known mixing methods can be used. In a case where step (a)is performed, a raw material comprising Nb (hereinafter, also referredto as “Nb raw material”) in the present embodiment is preferablyprepared separately from the aqueous mixed liquid (A). That is, in thepresent embodiment, the aqueous mixed liquid (A) preferably does notcontain Nb.

Examples of the Mo raw material include, but are not limited to,ammonium heptamolybdate [(NH₄)₆Mo₇O₂₄.4H₂O], molybdenum trioxide [MoO₃],phosphomolybdic acid [H₃PMo₁₂O₄₀], silicomolybdic acid [H₄SiMo₁₂O₄₀],and molybdenum pentachloride [MoCl₅]. Among these, ammoniumheptamolybdate [(NH₄)₆Mo₇O₂₄.4H₂O] is preferable. The Mo raw materialmay be these compounds or may be a solution obtained by dissolving thecompounds in a solvent.

Examples of the V raw material include, but are not limited to, ammoniummetavanadate [NH₄VO₃], vanadium pentoxide [V₂O₅], and vanadium chlorides[VCl₄, VCl₃]. Among these, ammonium metavanadate [NH₄VO₃] is preferable.The V raw material may be these compounds or may be a solution obtainedby dissolving the compounds in a solvent.

Examples of the Sb raw material include, but are not limited to,antimony oxides [Sb₂O₃, Sb₂O₅], antimonious acid [HSbO₂], antimonic acid[HSbO₃], ammonium antimonate [(NH₄)SbO₃], antimony chloride [Sb₂Cl₃],organic acid salts such as a tartaric acid salt of antimony, and metalantimony. Among these, diantimony trioxide [Sb₂O₃] is preferable. The Sbraw material may be these compounds or may be a solution obtained bydissolving the compounds in a solvent.

[Step (b): Mixing Step]

In step (b) in the present embodiment, the aqueous mixed liquid (A), theNb raw material, and, if necessary, the carrier raw material and a rawmaterial for an additional element or elements constituting the catalystare mixed to thereby obtain an aqueous mixed liquid (N). It is to benoted that the mixing method is not particularly limited, and knownmixing methods can be used. It is to be noted that the carrier rawmaterial is a raw material which becomes a carrier in the oxidecatalyst.

The carrier raw material in the present embodiment preferably containssilica sol. Examples of silica sol include acidic sol and basic sol, butany silica sol may be used and basic silica sol is more preferable. Thecarrier raw material preferably contains 30% by mass or more, morepreferably 30% by mass or more and 70% by mass or less, and still morepreferably 40% by mass or more and 60% by mass or less, of silica sol interms of SiO₂ based on the total amount (100% by mass) of the carrierraw material.

In step (b), it is preferable that the carrier raw material furthercontain powdery silica. This powdery silica becomes part of the silicaraw material together with silica sol.

Examples of the carrier raw material include aluminum oxide, titaniumoxide, and zirconium oxide in addition to silica sol, powdery silica,and the like. The carrier raw materials may be used singly, or two ormore thereof may be used together. A preferred carrier raw material issilica.

In step (b), the silica sol is preferably 30% by mass or more and 70% bymass or less, more preferably 40% by mass or more and 60% by mass orless, and still more preferably 45% by mass or more and 55% by mass orless, in terms of SiO₂ based on the total amount (100% by mass) ofsilica sol and powdery silica. When the silica sol is 30% by mass ormore, there is a tendency that deterioration of the attrition resistanceof the oxide catalyst is thereby suppressed, and when the silica sol is70% by mass or less, there is a tendency that deterioration of theperformance of the oxide catalyst is thereby suppressed.

Examples of the Nb raw material include, but are not limited to, niobicacid, inorganic acid salts of niobium, and organic acid salts ofniobium. Among these, niobic acid is preferable. Niobic acid isrepresented by formula Nb₂O₅.nH₂O and is also called a niobium hydroxideor a niobium oxide compound.

The Nb raw material preferably contains water. The Nb raw materialcontaining water is also referred to as a Nb raw material liquid. Onthis occasion, the ratio between water and Nb contained (Nb (mol)/Water(kg)) is more preferably set to 0.1 or more and 10 or less, still morepreferably 0.3 or more and 5.0 or less, from the viewpoint ofstabilizing the Nb raw material liquid or other viewpoints. In addition,the Nb raw material liquid may contain an organic acid salt or a freeorganic acid. The organic acid is not particularly limited, but oxalicacid is preferable. The molar ratio of the organic acid to niobium inthe Nb raw material (organic acid/niobium) is preferably 1.0 or more and4.0 or less.

The method of allowing the Nb raw material to contain water and theorganic acid is not particularly limited, and water and the organic acidmay be mixed in any order. In addition, the above-described mixing maybe performed at any temperature as long as the temperature is equal toor more than a temperature at which the Nb raw material liquidcontaining water does not freeze and equal to or less than a temperatureat which the Nb raw material liquid containing water is not boiled.However, from the viewpoint of operability of mixing and otherviewpoints, the mixing is preferably performed at room temperature.

The Nb raw material liquid may further contain hydrogen peroxide water.

In the raw material preparation step and/or the aging step, an operationof facilitating precipitation of Nb is performed in the presentembodiment. Conventionally, it has been considered that whenprecipitation of Nb is performed as slowly as possible to disperse Nbfinely in the aqueous mixed liquid (N), the aqueous mixed liquid becomesmore uniform, and the performance of a resultant catalyst also becomesmore favorable.

In contrast, in the present embodiment, it has been found that eventhough precipitation of Nb is made fast as described above, ahigh-performance oxide catalyst is obtained in a relatively short time.Particularly in a case where various conditions in the operation areadjusted as will be described later, it has been found that thesetendencies become remarkable.

The aspect (I) for facilitating precipitation of Nb is the followingoperation.

In the raw material preparation step, the aqueous mixed liquid isprepared by mixing the Nb raw material liquid comprising Nb with theMoVSb raw material liquid comprising Mo, V, and Sb, wherein ammonia isadded to at least one of the MoVSb raw material liquid, the Nb rawmaterial liquid, and the aqueous mixed liquid such that a molar ratio interms of NH₃/Nb in the aqueous mixed liquid is adjusted to be 0.7 ormore, and in the aging step, the temperature of the aqueous mixed liquidis adjusted to more than 50° C.

The molar ratio is more preferably 0.8 or more and 7 or less, still morepreferably 0.9 or more and 6 or less. By adding ammonia to the aqueousmixed liquid (N) such that the molar ratio in terms of NH₃/Nb becomes 7or less, there is a tendency that precipitation of Nb is facilitated inthe range where the favorable catalyst performance is kept, there is atendency that it can be prevented that the proper oxidation-reductionstates of the metal components in the liquid cannot be maintainedbecause NH₃ decomposes hydrogen peroxide which can be contained in theaqueous mixed liquid (N), and there is also a tendency that it can beprevented that the shape of the catalyst particle becomes distortedbecause the viscosity of the aqueous mixed liquid increases to make ithard to feed the aqueous mixed liquid in the drying step. It is to benoted that NH₃ at the time when the molar ratio in terms of NH₃/Nb iscalculated means the added ammonia and does not include an ammoniumsalt, such as ammonium heptamolybdate, ammonium metavanadate, orammonium metatungstate, in the Mo raw material, the V raw material, theSb raw material, the Nb raw material, or the Z raw material.

Ammonia is preferably added at each stage after preparing the aqueousmixed liquid (A), or is preferably added to the aqueous mixed liquid(N). That is, ammonia may be added at any stage after preparing theaqueous mixed liquid (A), and the order of addition of ammonia andaddition of the Nb raw material liquid, silica sol, powdery silica rawmaterial, and the like does not matter. Ammonia may be added immediatelyafter obtaining the aqueous mixed liquid (A), may be added after Nb ismixed with the aqueous mixed liquid (A), may be added after silica solis added to the aqueous mixed liquid (A), or may be added immediatelybefore the drying step. In addition, ammonia may be added into the Nbraw material liquid or silica sol.

The form of ammonia to be added is not particularly limited, but ammoniawater which is easy to handle is preferably used. Ammonia water can beused by appropriately selecting the concentration from among generalconcentrations.

The aspect (II) for facilitating precipitation of Nb is the followingoperation.

In the aging step, the temperature of the aqueous mixed liquid isadjusted to more than 65° C.

As will be described later, Nb forms a complex by the dicarboxylic acidand hydrogen peroxide to be stabilized in a dissolved state. By settingthe temperature after adding Nb to more than 65° C., there is a tendencythat decomposition of the complex progresses, so that precipitation ofNb can be effectively facilitated. From the viewpoint of moderatelyfacilitating precipitation of Nb, the temperature after adding Nb ispreferably set to more than 65° C. In addition, the above-describedoperation is particularly preferably performed as the step of subjectingthe aqueous mixed liquid (N) to aging, which will be described later.Further, from the viewpoint of not allowing the precipitation toprogress excessively and from the viewpoint of preventing theconcentration of the other metal components in the aqueous mixed liquidfrom becoming excessively high due to evaporation or boiling of water,the temperature is preferably set to 100° C. or less, more preferably90° C. or less, and still more preferably 80° C. or less. In addition,from the same reasons, the time to keep the temperature at more than 65°C. is preferably 1 minute or more and 5 hours or less.

The aspect (III) for facilitating precipitation of Nb is the followingoperation.

In the raw material preparation step, the aqueous mixed liquid isprepared by mixing the Nb raw material liquid comprising Nb with theMoVSb raw material liquid comprising Mo, V, and Sb, and here a molarratio in terms of H₂O₂/Nb in the Nb raw material liquid is adjusted toless than 0.2, and in the aging step, the temperature of the aqueousmixed liquid is adjusted to more than 50° C.

That is, in this aspect, a small amount of hydrogen peroxide may beadded to the Nb raw material liquid, or hydrogen peroxide do not have tobe added to the Nb raw material liquid. Hydrogen peroxide stabilizes Nbin a dissolved state by forming a complex with the Nb raw material, andtherefore when the molar ratio is 1.8 or more, there is a tendency thatprecipitation of Nb is inhibited. On the other hand, when the molarratio is set to less than 0.2, there is a tendency that the degree ofstability of the complex composed of Nb, hydrogen peroxide, and thedicarboxylic acid is lowered, so that precipitation of Nb can beeffectively facilitated. The molar ratio is more preferably set to lessthan 0.15, still more preferably less than 0.10.

In the present embodiment, at least one of the above-described aspects(I) to (III) may be selected and carried out, or a plurality of theabove-described aspects (I) to (III) may be appropriately combined andcarried out.

In step (a) and/or step (b), a raw material containing at least oneelement (hereinafter, also referred to as “component Z”) selected fromthe group consisting of W, La, Ce, Yb, and Y may be further mixed.

The Z raw material is not limited to the following as long as it is asubstance containing a component Z, and examples thereof include: acompound containing a component Z; and a metal of the component Z, themetal being made soluble by an adequate reagent. Examples of thecompound containing a component Z include, but are not limited to,ammonium salts, nitric acid salts, carboxylic acid salts, ammoniumcarboxylates, peroxocarboxylic acid salts, ammonium peroxocarboxylates,halogenated ammonium salts, halides, acetylacetonate, and alkoxides.Among these, water-soluble raw materials such as nitric acid salts andcarboxylic acid salts are preferable. It is to be noted thatparticularly when Z is W, the Z raw material is also referred to as a Wraw material. The same applies to a La raw material, a Ce raw material,an Yb raw material, and an Y raw material.

In step (a) and/or step (b), the raw material ratio is preferablyregulated such that the oxide catalyst obtained through step (d), whichwill be described later, has a composition represented by the followingformula (1). By using the oxide catalyst having a compositionrepresented by the following formula (1), there is a tendency that theyield of an unsaturated nitrile is further improved.

MoV_(a)Sb_(b)Nb_(c)Z_(d)O_(n)   (1)

wherein Z represents at least one element selected from the groupconsisting of W, La, Ce, Yb, and Y; a, b, c, and d represent values inthe ranges of 0.01≤a≤0.35, 0.01≤b≤0.35, 0.01≤c≤0.20, and 0.00≤d≤0.10,respectively; n represents a value satisfying a balance of atomicvalences; preferably 0.05≤a≤0.33, 0.05≤b≤0.33, 0.02≤c≤0.19, and0.001≤d≤0.09; and more preferably 0.10≤a≤0.30, 0.10≤b≤0.30, 0.05≤c≤0.18,and 0.002≤d≤0.08.

The composition of the oxide catalyst which is obtained after step (d)may be different from the composition of the oxide catalyst which isfinally obtained. That is, the composition of a protrusion, which willbe described later, of the oxide catalyst and the composition of themain body of the oxide catalyst are different because, in a case wherestep (e) of removing this protrusion is included, the composition of theoxide catalyst before step (e) is changed after step (e). In step (a)and/or step (b), the composition ratio is preferably set inconsideration of the change as well.

The “protrusion” in the present specification refers to matter that hasoozed out at and/or adhered to the surface of a calcined body obtainedthrough main calcination, which will be described later, or matter thathas protruded from and/or adhered to the surface of a calcined body.

Hereinafter, in step (a) and/or step (b), description will be madetaking as an example a case where the aqueous mixed liquid (B)comprising a Mo raw material, a V raw material, an Sb raw material, a Nbraw material, a carrier raw material, and a Z raw material is preparedusing water as a solvent and/or a dispersion medium. However, step (a)and/or step (b) are not limited to this.

In step (a), the aqueous mixed liquid (A) can be prepared by adding theMo raw material, the V raw material, the Sb raw material, and the Z rawmaterial to water and heating a resultant mixture. When the aqueousmixed liquid (A) is prepared, the heating temperature and the heatingtime are preferably adjusted in such a way as to create a state in whichrespective raw materials are sufficiently soluble. Specifically, theheating temperature is preferably 70° C. or more and 100° C. or less,and the heating time is preferably 30 minutes or more and 5 hours orless. On this occasion, the aqueous mixed liquid (A) is preferably beingstirred such that the raw materials easily dissolve. On this occasion,the atmosphere for preparing the aqueous mixed liquid (A) may be an airatmosphere but can be a nitrogen atmosphere from the viewpoint ofadjusting the oxidation number of the resultant oxide catalyst. Theaqueous mixed liquid (A) which is in a state after completion of theabove-described heating is also referred to as an aqueous mixed liquid(A′). The temperature of the aqueous mixed liquid (A′) is preferablyheld at 20° C. or more and 80° C. or less, and more preferably held at40° C. or more and 80° C. or less. When the temperature of the aqueousmixed liquid (A′) is 20° C. or more, there is a tendency that theprecipitation of metal species dissolving in the aqueous mixed liquid(A′) is thereby unlikely to occur.

Subsequently, a carrier raw material containing silica sol can be addedto the aqueous mixed liquid (A) or the aqueous mixed liquid (A′). Amongthese, silica sol is preferably added to the aqueous mixed liquid (A′).Silica sol functions as a carrier when it is made into an oxidecatalyst. The temperature at the point in time when silica sol is addedis preferably 80° C. or less. In a case where silica sol is added at 80°C. or less, there is a tendency that the stability of the silica sol isrelatively high to suppress gelation of the aqueous mixed liquid (B).The timing of adding silica sol may be at the point in time when agingis started, which will be described later, may be in the middle ofaging, or may be immediately before drying the aqueous mixed liquid (B).

Further, from the viewpoint of adjusting the oxidation number of acomplex oxide in the resultant oxide catalyst, if necessary, anappropriate amount of hydrogen peroxide water (H₂O₂) is preferably addedto the aqueous mixed liquid (A) or the aqueous mixed liquid (A′). Withrespect to the timing of adding hydrogen peroxide water, hydrogenperoxide water may be added to the aqueous mixed liquid (A) or theaqueous mixed liquid (A′) itself, may be added in the middle ofpreparing the aqueous mixed liquid (A) or the aqueous mixed liquid (A′),or may be added before or after adding silica sol. On this occasion,from the viewpoint of adjusting the oxidation number of the resultantoxide catalyst in a proper range, the amount of addition of hydrogenperoxide water is 0.01 or more and 5.0 or less, more preferably 0.5 ormore and 3.0 or less, and still more preferably 1.0 or more and 2.5 orless as a molar ratio of hydrogen peroxide water to Sb (H₂O₂/Sb).

Conditions (heating temperature and heating time) of a treatment whichcan be performed on the aqueous mixed liquid after adding hydrogenperoxide water to the aqueous mixed liquid (A) or the aqueous mixedliquid (A′) (hereinafter, also referred to as “aqueous mixed liquid(A″)”) are preferably adjusted in such a way as to create a state inwhich a liquid-phase oxidation reaction by hydrogen peroxide cansufficiently progress. Specifically, the heating temperature ispreferably 20° C. or more and 80° C. or less, and the heating time ispreferably 5 minutes or more and 4 hours or less. Similarly, the numberof revolutions during stirring at the time of heating can be adjusted toa moderate number of revolutions at which hydrogen peroxide water isuniformly mixed in the liquid and a sufficient liquid-phase oxidationreaction by hydrogen peroxide water easily progresses. From theviewpoint of allowing the liquid-phase oxidation reaction by hydrogenperoxide water to progress uniformly and sufficiently, the stirringstate is preferably kept during heating.

Next, the Nb raw material liquid is preferably prepared as an aqueousmixed liquid (N₀) by heating and stirring the Nb raw material and adicarboxylic acid in water. Examples of the dicarboxylic acid include,but are not limited to, oxalic acid [(COOH)₂]. Subsequently, an aqueousmixed liquid (N₁) is preferably prepared by adding hydrogen peroxidewater to the aqueous mixed liquid (N₀). On this occasion, the molarratio of hydrogen peroxide water to Nb (H₂O₂/Nb) in the aqueous mixedliquid (N₁) is preferably set to less than 0.2 from the viewpoint ofmoderately facilitating precipitation of Nb, properly regulating theoxidation-reduction states of constituent elements of the oxidecatalyst, making the catalyst performance of the resultant oxidecatalyst proper, and other viewpoints.

Subsequently, the aqueous mixed liquid (N) can be obtained by mixing theaqueous mixed liquid (A), the aqueous mixed liquid (A′), or the aqueousmixed liquid (A″) with the aqueous mixed liquid (N₀) or the aqueousmixed liquid (N₁) in conformity to the aimed composition. On thisoccasion, ammonia, the W raw material, or powdery silica may further bemixed.

In addition, the silica raw material may be mixed in the aqueous mixedliquid (N₀) or the aqueous mixed liquid (N₁) in advance. The order ofmixing the aqueous mixed liquid (N₀) or the aqueous mixed liquid (N₁)with the silica raw material is not particularly limited. The silica rawmaterial may be added to the aqueous mixed liquid (N₀) or the aqueousmixed liquid (N₁), or the aqueous mixed liquid (N₀) or the aqueous mixedliquid (N₁) may be added to the silica raw material. Among these, thesilica raw material may more preferably be added to the aqueous mixedliquid (N₀) or the aqueous mixed liquid (N₁) from the viewpoint ofsuppressing precipitation of Nb in the aqueous mixed liquid (N₀) or theaqueous mixed liquid (N₁). In addition, a resultant mixture may be leftto stand or stirred after the addition, and further, an ultrasonictreatment may be performed with a homogenizer or the like. On thisoccasion, part of the other metal raw materials may be added to theaqueous mixed liquid (N₀) or the aqueous mixed liquid (N₁) in advance,or part of the other metal raw materials may be added to the silica rawmaterial in advance. The other metal raw materials refer to the Mo rawmaterial, the V raw material, the Sb raw material, the W raw material,and the Z raw material. In addition, the amount of addition of the othermetal raw materials on this occasion is preferably less than 50% bymass, more preferably 0.0% by mass or more and 40% by mass or less, andstill more preferably 0.0% by mass or more and 30% by mass or less,based on the total amount of the metal raw materials which are finallyadded.

From the viewpoint of making the catalyst performance proper, powderysilica is preferably added to the “aqueous mixed liquid (A″)” or a“solution obtained by mixing the W raw material into the aqueous mixedliquid (B).” In addition, powdery silica can be added as it is, but ismore preferably added as a liquid in which the powdery silica isdispersed in water, that is, as a powdery silica-containing suspension.The concentration of powdery silica in the powdery silica-containingsuspension on this occasion is preferably 1.0% by mass or more and 30%by mass or less, and more preferably 3.0% by mass or more and 20% bymass or less. When the concentration of powdery silica is 1.0% by massor more, there is a tendency that it can be thereby suppressed that theshape of the catalyst particle becomes distorted due to a low viscosityof the aqueous mixed liquid (B). In addition, there is a tendency thatoccurrence of a depression in the catalyst particle can also besuppressed. When the concentration of powdery silica is 30% by mass orless, there is a tendency that gelation of the aqueous mixed liquid (B)and clogging of the aqueous mixed liquid (B) in piping, the gelation andthe clogging being attributable to a high viscosity of the aqueous mixedliquid (B), can be thereby suppressed, and there is a tendency that thedried powder can be thereby easily obtained. Further, there is atendency that the performance of the oxide catalyst is further improved.

Ammonia can be added to the aqueous mixed liquid (A), (A′), (A″), or (B)in order to facilitate precipitation of Nb. From the viewpoint ofproperly keeping the dissolution state of the metals in the aqueousmixed liquid (A), the viewpoint of effectively facilitatingprecipitation of Nb, and other viewpoints, ammonia is more preferablyadded to the aqueous mixed liquid (B). Part of ammonia may be addedsimultaneously with silica sol. The timing of addition to the aqueousmixed liquid (B) can be appropriately adjusted.

As the amount of NH₃ to be added, addition in an amount that makes themolar ratio in terms of NH₃/Nb in the aqueous mixed liquid (B) 0.7 ormore and 7 or less is preferable. The molar ratio is more preferably 0.8or more and 6 or less, and still more preferably 0.9 or more and 5.5 orless. By setting the molar ratio to 7 or less, precipitation of Nb canbe facilitated in the range where favorable catalyst performance iskept, it can be prevented that the proper oxidation-reduction states ofthe metal components in the liquid cannot be maintained because NH₃decomposes hydrogen peroxide in the aqueous mixed liquid, and it can beprevented that the shape of the catalyst particle becomes distortedbecause the viscosity of the aqueous mixed liquid increases to make ithard to feed the aqueous mixed liquid in the drying step.

[Aging Step]

In the present embodiment, the resultant aqueous mixed liquid (B) isprovided for an aging treatment. Aging of the aqueous mixed liquid (B)refers to leaving the aqueous mixed liquid (B) to stand or stirring theaqueous mixed liquid (B) for a predetermined time under the temperaturecondition at more than 30° C. The aging time is preferably 5 minutes ormore and 50 hours or less, and more preferably 5 minutes or more and 3hours or less. When the aging time is in the range, there is a tendencythat the aqueous mixed liquid (B) having a suitable oxidation-reductionstate (potential) becomes easily formed, and the catalyst performance ofa resultant complex oxide is further improved.

In a case where the oxide catalyst is industrially produced via dryingwith a spray-drier herein, the treatment speed of the spray drierusually controls the speed of production, and there is a tendency thatit takes time for the spray-drying of all the aqueous mixed liquid (B)to be completed after part of the mixed liquid is spray-dried. Duringthe spray-drying, aging of the aqueous mixed liquid which has not beensubjected to the spray-drying treatment yet is continued. Accordingly,the aging time not only includes the aging time before drying in step(c), which will be described later, but also includes the time from thestart to the completion of drying.

In addition, the aging temperature is set to more than 30° C. from theviewpoints of preventing condensation of the Mo component orprecipitation of the metal oxide due to V and the other metal species ora plurality of metals, making the oxidation states of Mo, V, and theother metal species proper, and allowing precipitation of Nb to progressmoderately. The aging temperature is more preferably set to more than50° C., and still more preferably more than 54° C. In addition, theaging temperature is preferably more than 65° C. from the viewpoint offorming the aqueous mixed liquid (B) of a preferred embodiment whileallowing the speed of precipitation of Nb due to hydrolysis of a complexcontaining Nb and hydrogen peroxide to fall within a proper range, andis preferably set to 100° C. or less, more preferably 90° C. or less,and still more preferably 80° C. or less in order not to allow theprecipitation to progress excessively and in order to prevent theconcentration of the other metal components in the aqueous mixed liquidfrom becoming excessively high due to evaporation/boiling of water. Thatis, adjusting the temperature of the aqueous mixed liquid in the secondpreferred aspect described above is preferably performed in the agingstep. By extending the aging time, raising the temperature of aging, orcombining and performing these, the catalyst can be further reducedduring calcination.

In addition, according to diligent studies conducted by the presentinventors, it has been found that there is a tendency that the reductionrate of the catalyst after calcination and the oxidation-reductionpotential of the aqueous mixed liquid (B) have a certain correlation.When the oxidation-reduction potential of the aqueous mixed liquid (B)becomes high, the catalyst after calcination leans toward an oxidationdirection, and when the oxidation-reduction potential of the aqueousmixed liquid (B) becomes low, the catalyst after calcination leanstoward a reduction direction. The oxidation-reduction potential of theaqueous mixed liquid (B) can be measured by using, but not particularlylimited to, a potentiometer sold on the market. Specifically, theoxidation-reduction potential is measured by the method described inExamples, which will be described later.

[Step (c): Drying Step]

Step (c) of the present embodiment is a step of drying the aqueous mixedliquid (N), thereby obtaining a dried powder. Drying can be performed byknown methods and can also be conducted, for example, by spray-drying orevaporation to dryness. In a case where a fluidized bed reaction systemis adopted in a gas-phase catalytic oxidation reaction or gas-phasecatalytic ammoxidation reaction in which the oxide catalyst is used, afine, spherical dried powder is preferably obtained in step (c) from theviewpoint of making the fluidity in a reactor into a preferred state, orother viewpoints. From the viewpoint of obtaining a fine, sphericaldried powder, spray-drying is preferably adopted. Nebulization in thespray-drying method may be any of a centrifugal system, a two-fluidnozzle system, and a high-pressure nozzle system. As a heat source fordrying, air heated with steam, an electric heater, or the like can beused.

The spray velocity, the rate of feeding the aqueous mixed liquid (B),the number of revolutions of an atomizer in the case of a centrifugalsystem, and the like are preferably adjusted such that the size of aresultant dried powder becomes suitable. The average particle diameterof the dried powder is preferably 35 μm or more and 75 μm or less, morepreferably 40 μm or more and 70 μm or less, and still more preferably 45μm or more and 65 μm or less. The average particle diameter does notchange so much even after calcination. Examples of the method ofadjusting the average particle diameter of the dried powder include amethod of performing classification, which will be described inExamples.

[Step (d): Calcination Step]

In step (d) of the present embodiment, the dried powder is calcined, andan oxide catalyst is thereby obtained. As a calcination apparatus forcalcining the dried powder, a rotary furnace (rotary kiln) for examplecan be used. The shape of a calcination vessel in which the dried powderis calcined is not particularly limited, but the calcination vessel ispreferably pipe-shaped (calcination pipe) from the viewpoint of enablingcontinuous calcination, and more preferably cylindrically shaped. As aheating system, an external heating type is preferable from theviewpoint of easiness of adjusting the calcination temperature in such away as to make a temperature-raising pattern preferable, and an electricfurnace can be suitably used as an external heat source. The size, thematerial, and the like of the calcination pipe can be appropriatelyselected according to the calcination conditions and the quantity ofproduction.

In step (d), the calcination is desirably performed by being dividedinto two stages. When the first calcination is referred to as fist-stagecalcination, and the latter calcination is referred to as maincalcination, it is preferable that the pre-stage calcination beperformed in a temperature range of 250° C. or more and 400° C. or less,and the main calcination be performed in a temperature range of 450° C.or more and 700° C. or less. The pre-stage calcination and the maincalcination may be performed continuously, or the main calcination maybe performed afresh after the pre-stage calcination is once completed.Alternatively, each of the pre-stage calcination and the maincalcination may be divided into several stages.

With respect to the calcination atmosphere, the calcination may beperformed in an air atmosphere or under air circulation, but from theviewpoint of adjusting the oxidation-reduction state into a preferredone, at least part of the calcination is preferably performed while aninert gas, such as nitrogen, which does not substantially contain oxygenis circulated. In a case where the calcination is performed batch-wise,the supply rate of the inert gas is preferably 50 NL/hr. or more, morepreferably 50 NL/hr. or more and 5000 NL/hr. or less, and still morepreferably 50 NL/hr. or more and 3000 NL/hr. or less per kg of the driedpowder from the viewpoint of adjusting the oxidation-reduction stateinto a preferred one. The “NL” herein means volume of a gas measured atthe normal temperature and pressure conditions, namely at 0° C. and 1atm.

The reduction rate of a calcined body (pre-stage calcined body) afterthe pre-stage calcination is preferably 7.0% or more and 15% or less,more preferably 8.0% or more and 12% or less, and still more preferably9.0% or more and 12% or less. When the reduction rate is in this range,there is a tendency that the activity of the oxide catalyst is therebyfurther improved, and the catalyst production efficiency is therebyfurther improved. Examples of a method of controlling the reduction ratein a desired range include, but are not limited to, a method of changingthe pre-stage calcination temperature, a method of adding an oxidativecomponent such as oxygen into the atmosphere during the calcination, anda method of adding a reductive component into the atmosphere during thecalcination. In addition, these may be combined.

[Step (e): Removal Step]

In step (e) optionally performed in the present embodiment, a protrusionexisting at the surface of a particle of the oxide catalyst is removed.Most of the protrusions are protruded crystals of an oxide or otherimpurities. Particularly in the case of a calcined body containing aplurality of metals, an oxide having a composition which is differentfrom that of the crystal which forms most part of the calcined body maybe formed in some cases in a form such that the oxide has oozed out ofthe main body part of the calcined body. There is a tendency that such aprotrusion becomes a factor of lowering the fluidity. Therefore, byremoving the protrusion from the surface of the oxide catalyst, there isa tendency that the performance of the oxide catalyst gets higher. In acase where the removal of the protrusion is performed in a gram scale,the apparatus described below can be used. That is, a perpendicular tubeprovided with a holed board having at least one hole at the bottomportion thereof and having a paper filter installed at the upper portioncan be used. By loading the calcined body into this perpendicular tubeand circulating air from below, air flows from each hole to facilitatecontact among calcined bodies, and the removal of the protrusion isperformed.

[Oxide Catalyst]

The oxide catalyst according to the present embodiment is obtained bythe above-described method for producing an oxide catalyst. Theresultant oxide catalyst preferably has a composition represented by thefollowing formula (1).

MoV_(a)Sb_(b)Nb_(c)Z_(d)O_(n)   (1)

wherein Z represents at least one element selected from the groupconsisting of W, La, Ce, Yb, and Y; a, b, c, and d represent values inthe ranges of 0.01≤a≤0.35, 0.01≤b≤0.35, 0.01≤c≤0.20, and 0.00≤d≤0.10,respectively; and n represents a value satisfying a balance of atomicvalences.

The composition of the oxide catalyst can be measured with fluorescentX-ray analysis (trade name “RIX1000” manufactured by Rigaku Corporation,Cr tube, tube voltage of 50 kV, tube current of 50 mA).

The oxide catalyst preferably comprises 30% by mass or more and 70% bymass or less of a carrier based on the total amount (100% by mass) of acomposite body of the oxide catalyst and the carrier. To obtain theoxide catalyst that is in such a range, the oxide catalyst preferablyuses 30% by mass or more and 70% by mass or less, as the total amount,of silica, such as silica sol and powdery silica, in terms of SiO₂ basedon the total amount of the composite body, and the oxide catalyst maymore preferably use 40% by mass or more and 60% by mass or less ofsilica and may still more preferably use 45% by mass or more and 55% bymass or less of silica. When the oxide catalyst comprises 30% by mass ormore of the carrier based on the total amount of the composite body,there is a tendency that the strength of the composite body comprisingthe oxide catalyst is thereby further improved, and when the oxidecatalyst comprises 70% by mass or less of the carrier, there is atendency that the oxide catalyst thereby has a higher activity.

The content of the carrier in the oxide catalyst can be determined, forexample, by measurement with fluorescent X-ray analysis (trade name“RIX1000” manufactured by Rigaku Corporation, Cr tube, tube voltage of50 kV, tube current of 50 mA).

[Method for Producing Unsaturated Nitrile or Unsaturated Acid]

The method for producing an unsaturated nitrile according to the presentembodiment comprises: a step of obtaining an oxide catalyst by themethod for producing an oxide catalyst according to the presentembodiment; and a production step of producing an unsaturated nitrilethrough a gas-phase catalytic ammoxidation reaction of propane orisobutane in the presence of the produced oxide catalyst. In addition,the method for producing an unsaturated acid according to the presentembodiment comprises: a step of obtaining an oxide catalyst by themethod for producing an oxide catalyst according to the presentembodiment; and a production step of producing an unsaturated acidthrough a gas-phase catalytic oxidation reaction of propane or isobutanein the presence of the produced oxide catalyst. In addition, theproduction step is preferably a step of producing an unsaturated nitrilethrough a gas-phase catalytic ammoxidation reaction of propane orisobutane. Hereinafter, a method for producing acrylonitrile as theunsaturated nitrile using the oxide catalyst according to the presentembodiment filled in a reactor will be described.

<Gas-Phase Catalytic Oxidation Reaction and Gas-Phase CatalyticAmmoxidation Reaction>

Propane or isobutane, and oxygen are used for a gas-phase catalyticoxidation reaction, and propane or isobutane; ammonia; and oxygen areused for a gas-phase catalytic ammoxidation reaction. Among them,propane and ammonia do not necessarily have to be of high purity, andmay be industrial-grade gasses such as propane containing 3% by volumeof an impurity such as ethane, ethylene, n-butane, or isobutane; andammonia containing 3% by volume of an impurity such as water. Examplesof oxygen include, but are not limited to: air, oxygen-enriched air, andpure oxygen; and gases obtained by diluting these with an inert gas suchas helium, argon, carbon dioxide, or nitrogen, or water vapor. Amongthese, in the case of use in an industrial scale, air is preferablebecause of simplicity.

The reaction conditions in the gas-phase catalytic oxidation reactionare not particularly limited, and examples thereof include the followingconditions. The molar ratio of oxygen to be supplied for the reaction topropane or isobutane, (oxygen/(propane and isobutane)), is preferably0.1 or more and 6.0 or less, and more preferably 0.5 or more and 4.0 orless. The reaction temperature is preferably 300° C. or more and 500° C.or less, and more preferably 350° C. or more and 500° C. or less. Thereaction pressure is preferably 5.0×10⁴ Pa or more and 5.0×10⁵ Pa orless, and more preferably 1.0×10⁵ Pa or more and 3.0×10⁵ Pa or less. Thecontact time is preferably 0.1 sec·g/cm³ or more and 10 sec·g/cm³ orless, and more preferably 0.5 sec·g/cm³ or more and 5.0 sec·g/cm³ orless. By setting the reaction conditions to the ranges, there is atendency that production of a by-product is further suppressed, and theyield of an unsaturated nitrile can be further improved.

In the present embodiment, the contact time is defined by the followingexpression.

Contact time (sec·g/cm³)=(W/F)×273/(273+T)

W, F, and T herein are defined as follows.

-   -   W=amount (g) of catalyst filled    -   F=flow rate (Ncm³/sec) of raw material mixed gas at the normal        state (0° C., 1.013×10⁵ Pa)    -   T=reaction temperature (° C.)

The conversion rate of alkane such as propane or isobutane, and theunsaturated acid or unsaturated nitrile yield follow the followingdefinition.

Conversion rate (%) of alkane=(number of moles of alkanereacted)/(number of moles of alkane supplied)×100

Unsaturated acid or unsaturated nitrile yield (%)=(number of moles ofunsaturated acid or unsaturated nitrile produced)/(number of moles ofalkane supplied)×100

The reaction conditions in the gas-phase catalytic ammoxidation reactionare not particularly limited, and examples thereof include the followingconditions. The molar ratio of oxygen to be supplied for the reaction topropane or isobutane, (oxygen/(propane and isobutane)), is preferably0.1 or more and 6.0 or less, and more preferably 0.5 or more and 4.0 orless. The molar ratio of ammonia to be supplied for the reaction topropane or isobutane, (ammonia/(propane and isobutane)), is preferably0.3 or more and 1.5 or less, and more preferably 0.7 or more and 1.2 orless. The reaction temperature is preferably 320° C. or more and 500° C.or less, and more preferably 370° C. or more and 460° C. or less. Thereaction pressure is preferably 5.0×10⁴ Pa or more and 5.0×10⁵ Pa orless, and more preferably 1.0×10⁵ Pa or more and 3.0×10⁵ Pa or less. Thecontact time is preferably 0.1 sec·g/cm³ or more and 10 sec·g/c ³ orless, and more preferably 0.5 sec·g/cm³ or more and 5.0 sec·g/cm³ orless. By setting the reaction conditions to the ranges, there is atendency that production of a by-product is further suppressed, and theyield of an unsaturated nitrile can be further improved.

As a reaction system in the gas-phase catalytic oxidation reaction andthe gas-phase catalytic ammoxidation reaction, known systems such as afixed bed, a fluidized bed, and a moving bed can be adopted. Amongthese, a fluidized bed reactor in which the heat of reaction is easilyremoved is preferable. In addition, the gas-phase catalytic ammoxidationreaction may be a single current type or a recycling type.

EXAMPLES

Hereinafter, the present embodiment will be described in further detailgiving specific Examples and Comparative Examples, but the presentembodiment is not limited by the following Examples and ComparativeExamples within a range not exceeding the scope thereof. Measurement andevaluation of various physical properties in the Examples and theComparative Examples, which will be described later, were performedaccording to the following methods.

(Preparation Example) Aqueous Mixed Liquid (N₀)

An aqueous mixed liquid (N₀) was prepared according to the followingmethod. Into 10 kg of water, 1.420 kg of niobic acid containing 79.8% bymass of Nb₂O₅ and 5.134 kg of oxalic acid dihydrate (H₂C₂O₄.2H₂O) weremixed. The molar ratio of oxalic acid/niobium added was 4.8, and theconcentration of niobium added was 0.52 mol/kg. This liquid was heatedand stirred at 95° C. for 2 hours to thereby obtain a mixed liquidcontaining niobium dissolved therein. This mixed liquid was left tostand and cooled with ice, and thereafter a solid was separated bysuction filtration to obtain a uniform niobium mixed liquid. The molarratio of oxalic acid/niobium in this niobium mixed liquid was found tobe 2.340 by the analysis described below. The resultant niobium mixedliquid was used as an aqueous mixed liquid (N₀) in producing oxidecatalysts of Examples 1 to 12 and Comparative Examples 1 to 4 below.

(Physical Property 1) Concentration of Niobium and Concentration ofOxalic Acid

Into a melting pot, 10 g of the aqueous mixed liquid (N₀) obtained abovewas precisely weighed, and was dried at 95° C. overnight, and thereaftera heat treatment was performed at 600° C. for 1 hour to obtain 0.8125 gof Nb₂O₅. From this result, the concentration of niobium was found to be0.611 mol (Nb)/kg (aqueous mixed liquid (N₀)). In addition, 3 g of thisaqueous mixed liquid (N₀) was precisely weighed into a 300-mL glassbeaker, 200 mL of approximately 80° C. hot water was added thereto, andsubsequently 10 mL of 1:1 sulfuric acid was added thereto. A resultantmixed liquid was titrated under stirring using 1/4 N KMnO₄ while keepingthe liquid temperature at 70° C. on a hot stirrer. A point where aslight, light pink color by KMnO₄ continued for approximately 30 secondsor more was determined to be an end point. The concentration of oxalicacid was determined from the titer by calculation according to thefollowing formula and was found to be 1.430 mol (oxalic acid)/kg(aqueous mixed liquid (N₀)).

2KMnO₄+3H₂SO₄+5H₂C₂O₄→K₂SO₄+2MnSO₄+10CO₂+8H₂O

(Physical Property 2) Oxidation-Reduction Potential of Aqueous MixedLiquids (B)

The oxidation-reduction potential of the aqueous mixed liquids (B) wasmeasured using a potentiometer sold on the market (manufactured byDKK-TOA CORPORATION).

(Physical Property 3) Composition of Oxide Catalysts

The composition of the oxide catalysts was measured with fluorescentX-ray analysis (trade name “RIX1000” manufactured by Rigaku Corporation,Cr tube, tube voltage of 50 kV, tube current of 50 mA).

(Physical Property 4) Amount of Carrier

The amount of a carrier is defined as the amount of the carrier (% bymass) based on the total amount (100% by mass) of the oxide catalystobtained in each of the Examples and the Comparative Examples, whichwill be described later, and the resultant oxide catalyst was subjectedto measurement by fluorescent X-ray analysis (trade name “RIX1000”manufactured by Rigaku Corporation, Cr tube, tube voltage of 50 kV, tubecurrent of 50 mA) to determine the amount of the carrier.

(Evaluation) Yield of Acrylonitrile (Unsaturated Nitrile), ConversionRate of Propane

In the Examples and the Comparative Examples, the yield of acrylonitrilewas determined as follows. A gas of acrylonitrile the concentration ofwhich was already known was analyzed by gas chromatography (GC: productname “GC2014” manufactured by SHIMADZU CORPORATION) to get a calibrationcurve in advance, and thereafter a gas produced through the ammoxidationreaction was quantitatively injected into the GC to measure the numberof moles of acrylonitrile produced. The yield of acrylonitrile wasdetermined from the measured number of moles of acrylonitrile accordingto the following expression.

Yield (%) of acrylonitrile−(number of moles of acrylonitrileproduced)/(number of moles of propane supplied)×100

In addition, the conversion rate of propane was determined as follows. Agas of propane the concentration of which was already known was analyzedby the GC to get a calibration curve in advance, and thereafter a gasproduced through the ammoxidation reaction was quantitatively injectedinto the GC to measure the number of moles of unreacted propane. Theconversion rate of propane was determined from the measured number ofmoles of unreacted propane according to the following expression.

Conversion rate (%) of propane=((number of moles of propanesupplied)−(number of moles of unreacted propane))/(number of moles ofpropane supplied)×100

Example 1

An oxide catalyst represented by the composition formulaMo₁V_(0.19)Sb_(0.229)Nb_(0.109)W_(0.03)Ce_(0.008) was prepared accordingto the following method.

(Preparation Step) Aqueous Mixed Liquid (A′)

To 1669 g of water, 490.8 g of ammonium heptamolybdate[(NH₄)₆Mo₇O₂₄.4H₂O], 61.4 g of ammonium metavanadate [NH₄VO₃], 92.7 g ofdiantimony trioxide [Sb₂O₃], and 9.8 g of cerium nitrate [Ce(NO₃)₃.6H₂O]were added and heated at 95° C. for 1 hour while being stirred toprepare an aqueous mixed liquid (A′).

To 487.9 g of an aqueous mixed liquid (N₀) having a molar ratio ofoxalic acid/niobium of 2.340, 67.6 g of hydrogen peroxide watercontaining 30% by mass of H₂O₂ was added, and a resultant mixture wasstirred and mixed at room temperature for 10 minutes to prepare anaqueous mixed liquid (N₁). The molar ratio in terms of H₂O₂/Nb in theaqueous mixed liquid (N₁) was 2. The result is shown in Table 1.

(Mixing Step) Aqueous Mixed Liquid (B)

The resultant aqueous mixed liquid (A′) was cooled to 70° C., thereafterto the aqueous mixed liquid, 897.4 g of silica sol containing 34.1% bymass of SiO₂ and 0.3% by mass of NH₃ was added, further, 108.0 g ofhydrogen peroxide water containing 30% by mass of H₂O₂ was added, andstirring was continued at 60° C. for 1 minute. Next, the whole amount ofthe aqueous mixed liquid (N₁), 38.2 g of ammonium metatungstate aqueoussolution (purity of 50%), and a dispersion liquid obtained by dispersing294.0 g of powdery silica in 2646.0 g of water were added in sequence tothe aqueous mixed liquid (A′). The oxidation-reduction potential on thatoccasion (at the point in time when the target period started) wasmeasured with an ORP electrode (HM-31P, manufactured by DKK-TOACORPORATION) to find that the value was the same as the value of thepotential of the standard liquid described in Comparative Example 1,which will be described later.

(Aging Step)

An aqueous mixed liquid (B) in the form of a slurry was obtained byadding 20.3 g of 25% ammonia water 1 minute after the measurement andsubjecting a resultant mixture to aging by stirring at 60° C. for 2hours. The molar ratio in terms of NH₃/Nb in the aqueous mixed liquid(B) was 1.5. The oxidation-reduction potential 30 minutes after thepoint in time when the target period started (at the point in time whenthe target period ended) was measured to calculate a value (potentialdifference from standard liquid) which is obtained by subtracting theoxidation-reduction potential from the potential, at the same point intime, of the standard liquid which was subjected to aging under the sameconditions as those in Comparative Example 1. In addition, the amount ofpotential dropped in the target period was calculated by subtracting thepotential at the point in time when the target period ended from thepotential at the point in time when the target period started. Theresults are shown in Table 1.

(Drying Step) Dried Powder (C)

The resultant aqueous mixed liquid (B) was supplied to a centrifugalspray drier (the heat source for drying is air, and the same heat sourcefor drying was used in the following centrifugal spray driers) to bedried to obtain a fine, spherical dried powder (C). The temperature atthe inlet of the drier was 210° C., and the temperature at the outletwas 120° C.

The resultant dried powder (C) was classified using a sieve having anopening of 25 μm to obtain a dried powder (D) being a classifiedproduct. The average primary particle diameter was 54 μm. The averageparticle diameter was measured with “LS230,” trade name, manufactured byBeckman Coulter, Inc. (the following average particle diameters weremeasured in the same manner).

(Calcination Step) Oxide Catalyst (E)

The resultant dried powder (D) was supplied to a continuous SUScylindrical calcination pipe having a diameter (inner diameter; thefollowing diameters were the same) of 3 inches and a length of 89 cm ata supply rate of 80 g/hr in a rotary furnace. Into the calcination pipe,a nitrogen gas of 1.5 NL/min was allowed to flow in each of thedirection opposite to the direction of supplying the dried powder(namely countercurrent; the same applies to the following directionsopposite) and the same direction as the direction of supplying the driedpowder (namely, parallel current; the same applies to the following samedirections) to make the total flow rate 3.0 NL/min. The pre-stagecalcination was performed by setting the temperature of the furnace suchthat the temperature can be raised to 360° C. being the highestcalcination temperature in 4 hours while the calcination pipe wasrotated at a rate of 4 revolutions/min, and the temperature can be heldat 360° C. for 1 hour. A small amount of the pre-stage calcined bodycollected at the outlet of the calcination pipe was sampled and heatedto 400° C. in a nitrogen atmosphere, and thereafter the reduction ratewas measured and found to be 10.1%. The collected pre-stage calcinedbody was supplied to a continuous SUS calcination pipe having a diameterof 3 inches and a length of 89 cm at a supply rate of 60 g/hr in arotary furnace. Into the calcination pipe, a nitrogen gas of 1.1 NL/minwas allowed to flow in each of the direction opposite to the directionof supplying the dried powder and the same direction as the direction ofsupplying the dried powder to make the total flow rate 2.2 NL/min. Themain calcination was performed by setting the temperature of the furnacesuch that the temperature can be raised to 680° C. in 2 hours, held at680° C. for 2 hours, and thereafter lowered to 600° C. in 8 hours, andthus an oxide catalyst (E) was obtained.

(Removal Step)

Into a perpendicular tube (inner diameter of 41.6 mm, length of 70 cm),which is provided with a holed disk at the bottom portion thereof, theholed disk including 3 holes having a diameter of 1/64 inches, and whichhas a paper filter installed at the upper portion thereof, 50 g of theoxide catalyst (E) was loaded. Subsequently, air was circulated upwardfrom below via each hole of the perpendicular tube at room temperatureto facilitate contact among calcined bodies. The length of the aircurrent on that occasion in the flowing direction of the air current was56 mm, and the average linear velocity of the air current was 332 m/s. Aprotrusion did not exist in the oxide catalyst (E) obtained after 24hours.

(Production Step) Ammoxidation Reaction of Propane

Propane was subjected to a gas-phase catalytic ammoxidation reactionaccording to the following method using the oxide catalyst (E) obtainedabove. In a Vycor glass fluidized bed type reaction pipe having an innerdiameter of 25 mm, 38 g of the oxide catalyst was filled, and a mixedgas having a molar ratio of propane:ammonia:oxygen:helium=1:1:2.9:18 wassupplied at a contact time of 3.0 (sec·g/cm³), reaction temperature of445° C., and a reaction pressure of 40 kPa. The reaction yield ofacrylonitrile (AN), the potential difference from the standard liquid,and the amount of potential dropped each obtained when the reaction wasperformed for consecutive 10 days with respect to this oxide catalystare shown in Table 1.

Examples 2 to 4

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the amount of ammonia water added in Example 1 was changed to theamount described in Table 1. The potential difference from the standardliquid and the amount of potential dropped were also measured in thesame manner as in Example 1. The reaction yield of acrylonitrile (AN),the potential difference from the standard liquid, and the amount ofpotential dropped each obtained when the ammoxidation reaction ofpropane was performed in the same manner as in Example 1 with respect tothis oxide catalyst are shown in Table 1.

Examples 5 and 6

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the aqueous mixed liquid (N₁), the ammonium metatungstate aqueoussolution, and the dispersion liquid obtained by dispersing powderysilica in water were added in sequence to the aqueous mixed liquid (A′),thereafter the resultant mixture was subjected to aging by stirring atthe temperature described in Table 1 and for the time described in Table1, and an aqueous mixed liquid (B) in the form of a slurry was obtainedwithout adding ammonia water. The potential difference from the standardliquid and the amount of potential dropped were also measured in thesame manner as in Example 1. The reaction yield of acrylonitrile (AN),the potential difference from the standard liquid, and the amount ofpotential dropped each obtained when the ammoxidation reaction ofpropane was performed in the same manner as in Example 1 with respect tothis oxide catalyst are shown in Table 1.

Examples 7 and 8

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the amount of hydrogen peroxide water added to the Nb mixed liquidwas changed to the value in Table 1, and an aqueous mixed liquid (B) inthe form of a slurry was obtained without adding ammonia water. Thepotential difference from the standard liquid and the amount ofpotential dropped were measured at the potential between 90 minutes and120 minutes after the start of aging. The reaction yield ofacrylonitrile (AN), the potential difference from the standard liquid,and the amount of potential dropped each obtained when the ammoxidationreaction of propane was performed in the same manner as in Example 1with respect to this oxide catalyst are shown in Table 1.

Examples 9 to 11

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the amount of addition of hydrogen peroxide to the niobium mixedliquid, and the temperature and the time of aging were changed to thevalues shown in Table 1. The potential difference from the standardliquid and the amount of potential dropped were measured at thepotential between 90 minutes and 120 minutes after the start of aging.The reaction yield of acrylonitrile (AN), the potential difference fromthe standard liquid, and the amount of potential dropped each obtainedwhen the ammoxidation reaction of propane was performed in the samemanner as in Example 1 with respect to this oxide catalyst are shown inTable 1.

Example 12

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the addition of ammonia water was changed to be carried out 30minutes after adding the dispersion liquid obtained by dispersingpowdery silica in water to the aqueous mixed liquid (A′). The potentialdifference from the standard liquid and the amount of potential droppedwere measured for 30 minutes from the time immediately before addingammonia water till 30 minutes after that. The reaction yield ofacrylonitrile (AN), the potential difference from the standard liquid,and the amount of potential dropped each obtained when the ammoxidationreaction of propane was performed in the same manner as in Example 1with respect to this oxide catalyst are shown in Table 1.

Example 13

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the addition of ammonia water was changed to be carried out 60minutes after adding the dispersion liquid obtained by dispersingpowdery silica in water to the aqueous mixed liquid (A′). The potentialdifference from the standard liquid and the amount of potential droppedwere measured for 30 minutes from the time immediately before addingammonia water till 30 minutes after that. The reaction yield ofacrylonitrile (AN), the potential difference from the standard liquid,and the amount of potential dropped each obtained when the ammoxidationreaction of propane was performed in the same manner as in Example 1with respect to this oxide catalyst are shown in Table 1.

Example 14

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the addition of ammonia water was changed to be carried out afteradding silica sol to the aqueous mixed liquid (A′). The reaction yieldof acrylonitrile (AN), the potential difference from the standardliquid, and the amount of potential dropped each obtained when theammoxidation reaction of propane was performed in the same manner as inExample 1 with respect to this oxide catalyst are shown in Table 1.

Comparative Example 1

An oxide catalyst was produced in the same manner as in Example 1 exceptthat ammonia water in Example 1 was not added, and the temperature ofaging in Example 1 was changed to 55° C. That is, the aqueous mixedliquid which is prepared in Comparative Example 1 corresponds to thestandard liquid in Examples 1 to 16. The amount of potential dropped wasalso measured in the same manner as in Example 1. The reaction yield ofacrylonitrile (AN) and the amount of potential dropped each obtainedwhen the ammoxidation reaction of propane was performed in the samemanner as in Example 1 with respect to this oxide catalyst are shown inTable 1. In the preparation step and the aging step of ComparativeExample 1, the evaluation was such that an influence of added hydrogenperoxide was large, and therefore precipitation of Nb was notfacilitated.

Comparative Example 2

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the temperature of aging in Example 1 was changed to 30° C. Theamount of potential dropped was also measured in the same manner as inExample 1. The reaction yield of acrylonitrile (AN) and the amount ofpotential dropped each obtained when the ammoxidation reaction ofpropane was performed in the same manner as in Example 1 with respect tothis oxide catalyst are shown in Table 1.

Example 15

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the amount of ammonia water added in Example 1 was changed to theamount described in Table 1. The potential difference from the standardliquid and the amount of potential dropped were also measured in thesame manner as in Example 1. The reaction yield of acrylonitrile (AN),the potential difference from the standard liquid, and the amount ofpotential dropped each obtained when the ammoxidation reaction ofpropane was performed in the same manner as in Example 1 with respect tothis oxide catalyst are shown in Table 1.

Example 16

An oxide catalyst was produced in the same manner as in Example 1 exceptthat the aging temperature in Example 1 was changed to the temperaturedescribed in Table 1. The potential difference from the standard liquidand the amount of potential dropped were also measured in the samemanner as in Example 1. The reaction yield of acrylonitrile (AN), thepotential difference from the standard liquid, and the amount ofpotential dropped each obtained when the ammoxidation reaction ofpropane was performed in the same manner as in Example 1 with respect tothis oxide catalyst are shown in Table 1.

Example 17

An oxide catalyst was produced in the same manner as in Example 1 exceptthat a catalyst was prepared in such a way as to have a compositionMo₁V_(0.210)Sb_(0.259)Nb_(0.109)W_(0.03)Ce_(0.005) by performing thepreparation step and the mixing step as described below.

(Preparation Step) Aqueous Mixed Liquid (A′)

To 1807 g of water, 479.7 g of ammonium heptamolybdate[(NH₄)₆Mo₇O₂₄.4H₂O], 66.3 g of ammonium metavanadate [NH₄VO₃], 102.4 gof diantimony trioxide [Sb₂O₃], and 6.0 g of cerium nitrate[Ce(NO₃)₃.6H₂O] were added and heated at 95° C. for 1 hour while beingstirred to prepare an aqueous mixed liquid (A′).

To 454.8 g of an aqueous mixed liquid (N₀) having a molar ratio ofoxalic acid/niobium of 2.340, 67.6 g of hydrogen peroxide watercontaining 30% by mass of H₂O₂ was added, and a resultant mixture wasstirred and mixed at room temperature for 10 minutes to prepare anaqueous mixed liquid (N₁).

(Mixing Step) Aqueous Mixed Liquid (B)

The resultant aqueous mixed liquid (A′) was cooled to 70° C., thereafterto the aqueous mixed liquid, 897.4 g of silica sol containing 34.1% bymass of SiO₂ and 0.3% by mass of NH₃ was added, further, 119.3 g ofhydrogen peroxide water containing 30% by mass of H₂O₂ was added, andstirring was continued at 60° C. for 1 minute. Next, the whole amount ofthe aqueous mixed liquid (N₁), 37.4 g of ammonium metatungstate aqueoussolution (purity of 50%), and a dispersion liquid obtained by dispersing294.0 g of powdery silica in 2646.0 g of water were added in sequence tothe aqueous mixed liquid (A′). The oxidation-reduction potential on thatoccasion (at the point in time when the target period started) wasmeasured with an ORP electrode (HM-31P, manufactured by DKK-TOACORPORATION).

(Aging Step)

An aqueous mixed liquid (B) in the form of a slurry was obtained byadding 20.3 g of 25% ammonia water 1 minute after the measurement andsubjecting a resultant mixture to aging by stirring at 60° C. for 2hours. The molar ratio in terms of NH₃/Nb in the aqueous mixed liquid(B) was 1. The potential difference from the standard liquid and theamount of potential dropped were also measured in the same manner as inExample 1. The reaction yield of acrylonitrile (AN), the potentialdifference from the standard liquid, and the amount of potential droppedeach obtained when the ammoxidation reaction of propane was performed inthe same manner as in Example 1 with respect to this oxide catalyst areshown in Table 1.

Comparative Example 3

An oxide catalyst was produced in the same manner as in Example 1 exceptthat ammonia water in Example 17 was not added, and the temperature ofaging in Example 17 was changed to 55° C. That is, an aqueous mixedliquid which is prepared in Comparative Example 3 corresponds to thestandard liquid in Example 17. The potential difference from thestandard liquid and the amount of potential dropped were also measuredin the same manner as in Example 1. The reaction yield of acrylonitrile(AN), the potential difference from the standard liquid, and the amountof potential dropped each obtained when the ammoxidation reaction ofpropane was performed in the same manner as in Example 1 with respect tothis oxide catalyst are shown in Table 1.

Example 18

An oxide catalyst was produced in the same manner as in Example 1 exceptthat a catalyst was prepared in such a way as to have a compositionMo₁V_(0.190)Sb_(0.257)Nb_(0.110)W_(0.03)Ce_(0.005) by performing thepreparation step and the mixing step as described below.

(Preparation Step) Aqueous Mixed Liquid (A′)

To 1640 g of water, 482.7 g of ammonium heptamolybdate[(NH₄)₆Mo₇O₂₄.4H₂O], 60.4 g of ammonium metavanadate [NH₄VO₃], 101.7 gof diantimony trioxide [Sb₂O₃], and 6.0 g of cerium nitrate[Ce(NO₃)₃.6H₂O] were added and heated at 95° C. for 1 hour while beingstirred to prepare an aqueous mixed liquid (A′).

To 488.7 g of an aqueous mixed liquid (N₀) having a molar ratio ofoxalic acid/niobium of 2.340, 67.7 g of hydrogen peroxide watercontaining 30% by mass of H₂O₂ was added, and a resultant mixture wasstirred and mixed at room temperature for 10 minutes to prepare anaqueous mixed liquid (N₁).

(Mixing Step) Aqueous Mixed Liquid (B)

The resultant aqueous mixed liquid (A′) was cooled to 70° C., thereafterto the aqueous mixed liquid, 897.4 g of silica sol containing 34.1% bymass of SiO₂ and 0.3% by mass of NH₃ was added, further, 118.4 g ofhydrogen peroxide water containing 30% by mass of H₂O₂ was added, andstirring was continued at 60° C. for 1 minute. Next, the whole amount ofthe aqueous mixed liquid (N₁), 37.4 g of ammonium metatungstate aqueoussolution (purity of 50%), and a dispersion liquid obtained by dispersing294.0 g of powdery silica in 2646.0 g of water were added in sequence tothe aqueous mixed liquid (A′). The oxidation-reduction potential on thatoccasion (at the point in time when the target period started) wasmeasured with an ORP electrode (HM-31P, manufactured by DKK-TOACORPORATION).

(Aging Step)

An aqueous mixed liquid (B) in the form of a slurry was obtained byadding 20.3 g of 25% ammonia water 1 minute after the measurement andsubjecting a resultant mixture to aging by stirring at 60° C. for 2hours. The molar ratio in terms of NH₃/Nb in the aqueous mixed liquid(B) was 1. The potential difference from the standard liquid and theamount of potential dropped were also measured in the same manner as inExample 1. The reaction yield of acrylonitrile (AN), the potentialdifference from the standard liquid, and the amount of potential droppedeach obtained when the ammoxidation reaction of propane was performed inthe same manner as in Example 1 with respect to this oxide catalyst areshown in Table 1.

Comparative Example 4

An oxide catalyst was produced in the same manner as in Example 1 exceptthat ammonia water in Example 18 was not added, and the temperature ofaging in Example 18 was changed to 55° C. That is, an aqueous mixedliquid which is prepared in Comparative Example 4 corresponds to thestandard liquid in Example 18. The potential difference from thestandard liquid and the amount of potential dropped were also measuredin the same manner as in Example 1. The reaction yield of acrylonitrile(AN), the potential difference from the standard liquid, and the amountof potential dropped each obtained when the ammoxidation reaction ofpropane was performed in the same manner as in Example 1 with respect tothis oxide catalyst are shown in Table 1.

Comparative Example 5

An oxide catalyst was produced in the same manner as in ComparativeExample 1 except that the aging time was changed from 2 hours to 4hours. The potential difference from the standard liquid and the amountof potential dropped were also measured in the same manner as inExample 1. That is, an aqueous mixed liquid which is prepared inComparative Example 1 corresponds to the standard liquid in ComparativeExample 5. The reaction yield of acrylonitrile (AN), the potentialdifference from the standard liquid, and the amount of potential droppedeach obtained when the ammoxidation reaction of propane was performed inthe same manner as in Example 1 with respect to this oxide catalyst areshown in Table 1. It is to be noted that the amount of potential droppedafter 4 hours was 15 mV.

TABLE 1 (Potential of Amount Amount standard liquid)- of of H₂O₂(potential of sample for Amount addition water Aspect of measurement)(mV) (mV) of of Amount added to facilitation Point in time Point in timepotential NH₃ ammonia Aging of Nb mixed of pre- when target when targetdropped Requirement addition water temper- H₂O₂ liquid cipitation ANperiod period in target (a) and/ NH₃/Nb (g) ature H₂O₂/Nb (g) of Nbyield/% started ended Period or (b) Example 1 1.5 20.3 60° C. 2 67.6 (I)55.5 0 13 18 (b) Example 2 3 50.7 60° C. 2 67.6 (I) 55.2 0 25 30 (b)Example 3 5.3 97.3 60° C. 2 67.6 (I) 55.0 0 35 40 (b) Example 4 1 10.160° C. 2 67.6 (I) 55.2 0 9 14 (b) Example 5 0.5 0 68° C. 2 67.6 (II)55.1 0 23 28 (b) Example 6 0.5 0 75° C. 2 67.6 (II) 54.9 0 28 33 (b)Example 7 0.5 0 60° C. 0.1 3.4 (III) 55.4 40 40 5 (a) Example 8 0.5 060° C. 0 0 (III) 55.3 45 55 15 (a) and (b) Example 9 1.5 20.3 68° C. 0 0(I), (II), (III) 55.0 45 95 15 (a) and (b) Example 10 1.5 20.3 60° C.0.1 3.4 (I), (III) 55.6 40 60 25 (a) and (b) Example 11 1.5 20.3 68° C.0.1 3.4 (I), (II), (III) 55.1 40 80 45 (a) and (b) Example 12 1.5 20.360° C. 2 67.6 (I) 55.2 0 35 40 (b) Example 13 1.5 20.3 60° C. 2 67.6 (I)54.9 0 55 60 (b) Example 14 1.5 20.3 60° C. 2 67.6 (I) 54.7 30 50 20 (a)and (b) Example 15 6.5 121.6 60° C. 2 67.6 (I) 54.2 0 45 50 (b) Example16 1.5 20.3 52° C. 2 67.6 (I) 54.3 0 27 32 (b) Comparative 0.5 0 55° C.2 67.6 — 53.5 — — 5 — Example 1 Comparative 1.5 20.3 30° C. 2 67.6 —53.6 0 0 5 — Example 2 Example 17 1.7 20.3 60° C. 2 67.6 (I) 54.5 −1 1420 (b) Comparative 0.6 0 55° C. 2 67.6 — 52.7 — — 5 — Example 3 Example18 1.5 20.3 60° C. 2 67.6 (I) 55.0 2 14 17 (a) and (b) Comparative 0.5 055° C. 2 67.6 — 52.9 — — 6 — Example 4 Comparative 0.5 0 55° C. 2 67.6 —53.9 0 0 5 — Example 5

The “Aspect of facilitation” in Table 1 shows which of aspects (I) to(III) in the present embodiment each Example corresponds to. It is to benoted that when a plurality of aspects are satisfied, the aspects areshown together, and “−” means that the Example does not correspond toany of the aspects.

In addition, the “Requirement (a) or (b)” in Table 1 shows which of therequirements (a) and (b) in the present embodiment each Examplesatisfies. It is to be noted that when both of the requirements aresatisfied, the requirements are shown together, and “−” means thatneither of the requirements is satisfied.

The present application claims the priority based on Japanese PatentApplication (Japanese Patent Application No. 2016-178885) filed on Sep.13, 2016, the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The method for producing an oxide catalyst according to the presentinvention can be used for production of a catalyst for producing anunsaturated nitrile.

1. A method for producing an unsaturated nitrile, the method comprisingthe steps of: producing an oxide catalyst by following steps of: a rawmaterial preparation step of obtaining an aqueous mixed liquidcomprising Mo, V, Sb, and Nb; an aging step of subjecting the aqueousmixed liquid to aging at more than 30° C.; a drying step of drying theaqueous mixed liquid, thereby obtaining a dried powder; and acalcination step of calcining the dried powder, thereby obtaining theoxide catalyst, wherein, in the raw material preparation step and/or theaging step, precipitation of Nb is facilitated by performing at leastone operation selected from the group consisting of the following (I) to(III): (I) in the raw material preparation step, the aqueous mixedliquid is prepared by mixing a Nb raw material liquid comprising Nb witha MoVSb raw material liquid comprising Mo, V, and Sb, wherein ammonia isadded to at least one of the MoVSb raw material liquid, the Nb rawmaterial liquid, and the aqueous mixed liquid such that a molar ratio interms of NH₃/Nb in the aqueous mixed liquid is adjusted to be 0.7 ormore, and in the aging step, a temperature of the aqueous mixed liquidis adjusted to more than 50° C.; (II) in the aging step, a temperatureof the aqueous mixed liquid is adjusted to more than 65° C.; and (III)in the raw material preparation step, the aqueous mixed liquid isprepared by mixing a Nb raw material liquid comprising Nb with a MoVSbraw material liquid comprising Mo, V, and Sb, wherein a molar ratio interms of H₂O₇/Nb in the Nb raw material liquid is adjusted to less than0.2, and in the aging step, a temperature of the aqueous mixed liquid isadjusted to more than 50° C.; and further comprising a step of producingan unsaturated nitrile through a gas-phase catalytic ammoxidationreaction of propane or isobutane in a presence of the produced oxidecatalyst.
 2. A method for producing an unsaturated acid, the methodcomprising the steps of: producing an oxide catalyst by following stepsof: a raw material preparation step of obtaining an aqueous mixed liquidcomprising Mo, V, Sb, and Nb; an aging step of subjecting the aqueousmixed liquid to aging at more than 30° C.; a drying step of drying theaqueous mixed liquid, thereby obtaining a dried powder; and acalcination step of calcining the dried powder, thereby obtaining theoxide catalyst, wherein, in the raw material preparation step and/or theaging step, precipitation of Nb is facilitated by performing at leastone operation selected from the group consisting of the following (I) to(III): (I) in the raw material preparation step, the aqueous mixedliquid is prepared by mixing a Nb raw material liquid comprising Nb witha MoVSb raw material liquid comprising Mo, V, and Sb, wherein ammonia isadded to at least one of the MoVSb raw material liquid, the Nb rawmaterial liquid, and the aqueous mixed liquid such that a molar ratio interms of NH₃/Nb in the aqueous mixed liquid is adjusted to be 0.7 ormore, and in the aging step, a temperature of the aqueous mixed liquidis adjusted to more than 50° C.; (II) in the aging step, a temperatureof the aqueous mixed liquid is adjusted to more than 65° C.; and (III)in the raw material preparation step, the aqueous mixed liquid isprepared by mixing a Nb raw material liquid comprising Nb with a MoVSbraw material liquid comprising Mo, V, and Sb, wherein a molar ratio interms of H₂O₂/Nb in the Nb raw material liquid is adjusted to less than0.2, and in the aging step, a temperature of the aqueous mixed liquid isadjusted to more than 50° C.; and further comprising a step of producingan unsaturated acid through a gas-phase catalytic oxidation reaction ofpropane or isobutane in a presence of the produced oxide catalyst. 3.The method for producing an unsaturated nitrile according to claim 1,wherein the oxide catalyst has a composition represented by thefollowing formula (1):MoV_(a)Sb_(b)Nb_(c)Z_(d)O_(n)   (1) wherein Z represents at least oneelement selected from the group consisting of W, La, Ce, Yb, and Y; a,b, c, and d represent values in ranges of 0.01≤a≤0.35, 0.01≤b≤0.35,0.01≤c≤0.20, and 0.00≤d≤0.10, respectively; and n represents a valuesatisfying a balance of atomic valences.
 4. The method for producing anunsaturated nitrile according to claim 1, wherein the oxide catalystcomprises 30% by mass or more and 70% by mass or less of a carrier basedon a total amount of the oxide catalyst.
 5. The method for producing anunsaturated acid according to claim 2, wherein the oxide catalyst has acomposition represented by the following formula (1):MoV_(a)Sb_(b)Nb_(c)Z_(d)O_(n)   (1) wherein Z represents at least oneelement selected from the group consisting of W, La, Ce, Yb, and Y; a,b, c, and d represent values in ranges of 0.01≤a≤0.35, 0.01≤b≤0.35,0.01≤c≤0.20, and 0.00≤d≤0.10, respectively; and n represents a valuesatisfying a balance of atomic valences.
 6. The method for producing anunsaturated acid according to claim 2, wherein the oxide catalystcomprises 30% by mass or more and 70% by mass or less of a carrier basedon a total amount of the oxide catalyst.